Accuracy of a point-of-care blood gas analyzer in gastric tonometry measurements of intramucosal pH (pHi) and PCO2 gap

Purpose We assessed the accuracy of a point-of-care blood gas analyzer in providing data from saline samples obtained by gastrointestinal tonometry (Tonometrics Catheter; Tonometrics Division, Instrumentarium, Helsinki, Finland) for the calculation of intramucosal pH (pHi) and the P_CO2 gap (intramucosal P_CO2 – Pa_CO2).Methods We compared the point-of-care analyzer (Opti; AVL Medical Instruments, Schaffhausen, Switzerland; Opt) with a conventional analyzer (Compact 2 AVL Medical Instruments, Schaffhausen; Elect) in a clinical study (Elect being taking as the standard). In an in vitro study, P_CO2 data of tonometer saline (Pr_CO2) from Opt and Elect were compared with P_CO2 data from a continuous air tonometer (Tonocap Tonometrics Division, Instrumentarium) for a bottle containing a mixed P_CO2 gas. Data were evaluated by the Bland-Altman method.Results In the clinical study, the bias (B) and precision (P) were: B = 0.223 and P = 0.056 for pHi, B = –14.0 and P = 2.43 (mmHg) for Pr_CO2, and B = –16.7 and P = 2.6 (mmHg) for the P_CO2 gap (n = 27). In the in vitro study, the bias between the two values (Pr_CO2 and bottle P_CO2) was –1.98mmHg and precision was 1.23mmHg for Elect, but for Opt, these values were –22.09mmHg and 3.15mmHg, respectively (n = 18).Conclusion Opt is not suitable for measuring pHi and the P_CO2 gap because it does not provide an accurate P_CO2 for tonometry saline.Part of this study was presented at the 20th International Symposium on Intensive Care and Emergency Medicine (Brussels, March, 2000).